It is well known that anomalies in the shape of the eye can be the cause of visual disorders. Normal vision occurs when light passes through and is refracted by the cornea, the lens, and other portions of the eye, and converges at or near the retina.
In a myopic or near-sighted eye, the cornea is too steeply curved for the length of the eye. This curvature causes light rays to converge at a point before it reaches the retina. Distant objects, therefore, appear out-of-focus or blurry since the light rays are not in focus by the time they reach the retina. Approximately one in four persons have myopic vision.
In persons who are older, a condition called presbyopia occurs in which there is a diminished power of accommodation of the natural lens resulting from the loss of elasticity of the lens. Ordinarily the eye may vary its optical power by focusing the natural lens. However, with the loss of lens elasticity, the eye muscles cannot bend or focus the lens needed for clear vision of near objects. Typically presbyopia begins about the age of 40 and becomes significant after the age of 45.
Corrections for myopia and presbyopia have been attempted primarily through the use of prescriptive lenses in the form of glasses. Many adults wear bifocals or trifocals to correct their vision to see clearly at different distances. Generally, a bifocal lens is arranged such that the upper portion of the lens is used for distance vision and the lower portion for near vision. For reading, a person looks through the lower portion of the lens.
Additionally, available for the correction of myopia and presbyopia are hard, gas-permeable, and soft contact lenses. These contact lenses come in a variety of designs and provide bifocal correction. Also known for multi-vision correction are diffractive contact lenses where the surface of the lenses have invisible ridges molded into concentric circles. Generally, light passing through the lens is bent so that the wearer's near and distant vision is corrected. Few persons of older age, however, are able to adjust to the use of contact lenses. This is especially true as many older persons have trouble inserting and removing the contacts on a daily basis from their eyes.
Also, correction of myopia through the use of various corneal implants within the body of the cornea have been suggested. Various designs for such implants include solid and split-ring shaped, circular flexible body members and other types of ring-shaped devices that are adjustable. These implants are inserted within the body of the cornea for changing the shape of the cornea, thereby altering the its refractive power. Although these corneal implants attempt to correct for the myopic condition, they do not adequately accommodate for presbyopia.